Fiberglass has been used for many years in high temperature resistant electrical wire and cable constructions. Fiberglass has the advantages of being an enorganic material having a softening point above 800.degree. C. and yet is flexible in filament, yarn strands or fiber form and also in the form of woven or braided cloth, tapes or sleeves and the like such as disclosed in U.S. Pat. No. 5,154,954, the disclosure of which is incorporated herein by reference.
It has also been the practice to impregnate fiberglass electrical insulation with high temperature binders, varnishes, and resins of various kinds and types that in many cases tend to lower the softening point to less than 200.degree. C. and also characteristically tend to stiffen the insulated conductor or cable.
In some instances, high temperature resistant electrical insulation combine mica and fiberglass to provide resistance to temperatures of 450.degree. C. or higher such as disclosed in U.S. Pat. No. 3,629,024, the disclosure of which is incorporated herein by reference and in which mica is bonded to a fiberglass backing by a relatively hard and nonpliable resinous composition.
An example of a high temperature insulation system for electrical wire and cable products rated at 250.degree. C. is where the wire or conductor is provided with a taped or ram extruded coating of polytetrafluorelylene (PTFE) polymer about which a layer of fiberglass yarn is wrapped or served which is then enclosed by a fiberglass braid.
Thus, numerous high temperature products, including electrical wire and cable products, have been developed over the years using fiberglass, or impregnated fiberglass, or combinations of fiberglass with other inorganic materials such as mica.
One of the problems associated with fiberglass electrical insulation however, is that there is a tendency for the fiberglass fibers in close proximity to the conductor to string out and not break cleanly when the fiberglass is being cut through in order to strip the fiberglass from the conductor for making an electrical connection or the like.
One of the reasons contributing to the stringing tendency of the fiberglass fibers is that cutting blades are often sized so as not to contact the conductor itself, for fear of damaging the conductor, and thus may only partially cut through the last few remaining fibers of fiberglass in close proximity to the conductor causing the stripping process to be more costly and time consuming by having to remove the fiber strings separately.
It has been discovered that the stringing tendency of fiberglass fibers in close proximity to an electrical conductor from which the insulation is being stripped can be virtually eliminated and thus the strippability enhanced by treating fibers with a solution operative to render them sufficiently frangible upon heat aging to enhance the strippability of the fiberglass from the conductor of which our example has been found to be a solution containing sodium silicate.